Added test to dormitory-lib test for removal with wrong id
Added test to dormitory-lib test for removal with wrong id

The test now covers the case when a user tries to remove a dormitory or
a room with a wrong id.
refs #395

lukasjuhrich/pycroft,agdsn/pycroft,agdsn/pycroft,agdsn/pycroft,agdsn/pycroft,lukasjuhrich/pycroft,lukasjuhrich/pycroft,agdsn/pycroft,lukasjuhrich/pycroft